Learning new response sequences.

Four rats were required to press either a right or left lever to complete various three-response sequences. After extended exposure to a training sequence, subjects were shifted to a new target sequence. The new target sequences always differed from the previous sequence by the response required in the first or last position of the sequence. Subjects were repeatedly exposed to all possible combinations of training and new target sequences. Learning of new sequences occurred more rapidly when the change in the new target sequence was in the last position. Errors persisted longer in new sequences in which the change was in the first position. Extinction of the training sequence occured faster when the change was in the last position. Responses in the last position were considerably more sensitive to the shift to new target sequences than were responses in the first position. Even though response sequences may form new behavioral units from the training sequence, reinforcement and extinction acted differentially on the individual lever presses within new target sequences rather than on the sequences as a whole. These findings support the hypothesis that response strength is determined by contiguity to reinforcement.